In the art of machines for cold bending threaded rods into U-bolts, for example, of the general type disclosed in U.S. Pat. No. 4,936,131 issued to a co-inventor of the present invention, it is common to position an unthreaded center portion of a metal rod having opposite threaded end portions onto a mandrel or die and to bend the rod around the die by moving a pair of bending rollers along parallel linear paths on opposite sides of the die. The bending rollers are usually supported by arms which form part of a movable carriage actuated by a hydraulic cylinder. The arms are adjustable by a connecting adjustment screw extending from a hand wheel or crank for adjusting the spacing between the bending rollers to accommodate dies of different sizes and shapes and also for accommodating rods of different diameters.
The bending operation is produced by extending and retracting the carriage and the bending rollers so that the metal rod is bent into a generally U-shaped configuration to form a U-bolt. While the bending rollers form the U-bolt with parallel legs having the threaded end portions, when the carriage and bending rollers are retracted, the metal rod springs back slightly so that the legs are no longer precisely parallel and diverge outwardly by a slight angle.
U-bolt bending machines have been constructed wherein the bending rollers are carried by corresponding end portions of pivotally supported arms, and the arms are backed-up by corresponding rollers. The back-up rollers cause the arms and rod bending rollers to move inwardly or converge as the bending rollers move past the die in order to obtain overbending of the rod around the die. Thus when the arms and bending rollers are retracted, the leg portions spring back to substantially parallel positions. The backup rollers have also been supported by corresponding adjustable blocks in order to adjust the slightly converging paths of the bending rollers when the carriage moves from its retracted position to its extended position. Such a bending machine, which overbends the U-bolts to obtain substantially parallel legs, has been used for high volume production of one size U-bolts since substantial down time of the bending machine is required to adjust or reset the backup roller support blocks when a different mandrel is used or different diameter rods are to be bent into U-bolts. One such U-bolt bending machine was constructed and used by Turner's Alignment and Brake Service, Inc. in Muncie, Ind. and sold under the trademark "Arctic Bend".